<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        var car = null;
        alert(typeof car); //object

        if (car != null) {
            //执行操作
        }

        alert(null == undefined);//true

    </script>
</head>
<body>

</body>
</html>